FRR is a technology proposed by Internet Engineering Task Force (IETF) for local protection of a MPLS network. The technology provides fast protection switching capability for a Label Switched Path (LSP) by means of traffic engineering capability of the MPLS.
MPLS fast reroute is characterized by quick response, timely switching, assurance for smooth transition of service data, and decrease of service interruption. Local backup paths are established in advance, and then when any failure occurs, a device may quickly switch service to a backup path upon detecting the failure of a link or a node, thereby protecting a LSP from the failure of the link or the node and decreasing data loss. At the same time, the LSP's source node may attempt to find a new path for re-establishing a new LSP and switching data to the new path. Service data will be forwarded over a detour until a new LSP is established successfully.
There are mainly two existing modes for implementing point-to-point (P2P), i.e., unicast LSP fast reroute: 1:1 (one-for-one) protection mode and tunnel protection mode. In the one-for-one protection mode, a detour is established for each potential Point of Local Repair (PLR) in a protected LSP. In the tunnel protection mode, a bypass tunnel is established to protect multiple LSPs passing same nodes and links.
In the one-for-one protection mode, a primary LSP is established through a Resource Reservation Protocol-Traffic Engineering (RSVP-TE) signaling. The signaling for the establishment contains the LSP's protection characteristics including whether local protection is required, whether node protection is required, whether bandwidth protection is required, and properties of a backup LSP. Each node on the primary LSP except for destination nodes is a PLR. The PLR computes and establishes a backup LSP from the present PLR to the destination nodes of the primary LSP according to protection characteristics of the primary LSP and local policy, in order to protect its downstream link and node.
FIG. 1 is a schematic diagram for implementing unicast one-for-one fast reroute. As shown in FIG. 1, there are one primary LSP and two backup LSPs. The primary LSP is [R1, R2, R3, R4, R5, R6], the backup LSP1 is [R2, R7, R8, R9, R4, R5, R6], and the backup LSP2 is [R3, R8, R9, R5, R6]. When the link [R2->R3] fails, R2 may switch traffic from the primary LSP to the backup LSP1, and the traffic transmission path is changed to [R1, R2, R7, R8, R9, R4, R5, R6]. In this way, services are not interrupted due to failure of link [R2->R3].
FIG. 2 is a schematic diagram for implementing point-to-multipoint (P2MP), i.e. multicast one-for-one fast reroute. The basic concept lies in dividing a point-to-multipoint LSP into multiple point-to-point sub-LSPs. As shown in FIG. 2, there are four sub-LSPs: [S, A, B, d1], [S, A, B, E, d2], [S, A, C, D, d3], and [S, A, C, D, d4]. Backup LSPs are established for the sub-LSPs respectively according to existing point-to-point fast reroute mechanism, in order to protect the sub-LSPs.
The existing solution for implementing multicast fast reroute need establish backup LSPs for all sub-LSPs respectively in order to protect the sub-LSPs. Since links or nodes existing in respective sub-LSPs may overlap each other, it is likely to establish many redundant detours if backup LSPs are established for all the sub-LSPs respectively, hence consuming much protection bandwidth and wasting network resources.